I read IRC calls for step flashing that is 0.019″.  All three of the roofing wholesalers in my area who contractors get supplies from  each stock a different brand of aluminum step flashing that is 0.011″, or in one case it ranges from 0.011″ to 0.014″. I might be able to convince my contractor to deal directly with Raytec to order just a few boxes of 0.018″ thick step flashing, still less than IRC calls for but probably not a significant difference. I was not given a price as I’m not a contractor. I was told one box of 0.018″ gauge compared to one box of standard gauge would likely cost the contractor an estimated additional $100 to $150 more per box- but they admitted that was an off-the-cuff estimate. However, that would be an extra cost compared to standard thickness above an already inflated cost because the contractor would likely just purchase that thickness just for my house likely, so the cost per box is also higher if only getting a small number of boxes. I live in Climate Zone 4a, mixed-humid. (not near salt-water coastal area). I just don’t want the aluminum flashing to need replaced, and to re-experience the nightmare of a leaking roof long before the expected lifespan of the shingles ends. If I only need 3 or 4 boxes, do you think it would be worth asking the contractor to take the extra effort and time to procure the thicker step flashing, and for me to pay extra for it? Is it worth risking being perceived as a pain in the you know what? It is if it really makes a difference, but I’m not sure it will greatly affect the lifespan. I’m worried though as I read the lifespans for aluminum flashing ranges from 15 to 25 years, but supposedly the lifespan of the shingles can last longer. Since IRC states it should be 0.019″ thick, I’m surprised it is not commonly stocked around where I live, but then again maybe it really doesn’t matter much.